This invention relates to a method to produce chlorine dioxide and more in particular to a method to produce chlorine dioxide by reacting an alkali metal chlorate with a strong acid.
It has been found that chlorine dioxide can conveniently be used for the bleaching of wood pulp. Chlorine dioxide, however, is known to be an explosively endothermic compound. As such, it generally cannot be shipped safely from a manufacturer to the pulp mill consumer. Consequently, chlorine dioxide is usually generated on-site as required by the pulp mill.
Chlorine dioxide commonly is produced by the reduction of a chlorate salt by a chloride salt in an acidic medium. Although operable acids include hydrochloric, perchloric, phosphoric and sulfuric acids, from a commercial standpoint, sulfuric acid has been generally found to be most satisfactory.
Chlorine dioxide is produced from the reaction of sodium chlorate with sodium chloride in a sulfuric acid medium in accord with the equation: EQU 2NaClO.sub.3 + 2NaCl + 2H.sub.2 SO.sub.4 .fwdarw. 2Na.sub.2 SO.sub.4 + 2ClO.sub.2 + Cl.sub.2 + 2H.sub.2 O
alternatively, chlorine dioxide can be produced from the reaction of sodium chlorate with hydrogen chloride in a sulphuric acid medium in accordance with the equation:
2NaClO.sub.3 + 2HCl + H.sub.2 SO.sub.4 .fwdarw. Na.sub.2 SO.sub.4 + 2ClO.sub.2 + Cl.sub.2 + 2H.sub.2 O.
in both cases the production of chlorine dioxide using a sulphuric acid medium leads to the coproduction of sodium sulfate, the disposal of which poses an unsolved and increasingly more difficult environmental problem.
Canadian Pat. Nos. 956,784 and 969,735 describe processes to produce chlorine dioxide from the reaction of an alkali metal chlorate, such as sodium chlorate, and hydrochloric acid in accordance with the equation: EQU 2NaClO.sub.3 + 4HCl .fwdarw. 2NaCl + 2ClO.sub.2 + Cl.sub.2 + 2H.sub.2 O In such an HCl process the production of chlorine dioxide results in the coproduction of sodium chloride, which can be advantageously used as, for example, a feed stock for an electrolytic cell to produce sodium chlorate.
The known processes to produce chlorine dioxide by reacting an alkali metal chlorate with HCl have oftentimes not been commercially successful. It is desired, therefore, to provide an efficient process to form chlorine dioxide from an alkali metal chlorate without the production of an alkali metal sulfate.